Enhanced soft X-ray emission from carbon nanofibers irradiated with ultra-short laser pulses |
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| Authors: | U Chakravarty P A Naik B S Rao V Arora H Singhal G M Bhalerao A K Sinha P Tiwari P D Gupta |
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| Institution: | (1) Nanjing University, Nanjing, P.R. China;(2) World Precision Instruments, Inc., Sarasota, FL, USA;(3) University of Science & Technology, Beijing, P.R. China;(4) University of California, San Diego, CA, USA |
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| Abstract: | A comparative experimental study of the X-ray emission in the water-window spectral region has been performed using carbon
nanofibers (CNFs) of different sizes and graphite plate targets, irradiated with ultra-short (Ti:sapphire) laser pulses. More
than an order of magnitude enhancement in the X-ray yield is observed from CNFs of 60-nm diameter with respect to graphite
targets. The X-ray emission from CNFs of 160-nm diameter was also high. The integrated X-ray yield of these carbon-based targets
scales with the laser intensity (I
L) as IL ~ 1.3-1.4I_{\mathrm{L}}^{\sim 1.3-1.4} in the intensity range of 4×1016–4×1017 W/cm2. The effect of the laser pulse duration on the X-ray emission from the CNFs was also studied by varying the pulse duration
from 45 fs up to 3 ps at a constant fluence of 2×104 J/cm2. The optimum laser pulse duration for maximum X-ray emission increases with the diameter of the CNFs used. The results are
explained from physical considerations of heating and hydrodynamic expansion of the CNF plasma in which resonance field enhancement
takes place while passing through two times the critical density. The results add to the efforts towards achieving an efficient
low-cost water-window X-ray source for microscopy. |
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